Satellites play an important role in modern communications systems. Common communications such as telephone calls and television programming are transmitted and received using satellite communications systems. Communications satellites are typically placed in geostationary orbits around the Earth. However, limited frequency spectrum and insufficient orbital locations are impeding the expansion of satellite communications services. This problem is particularly severe over areas such as North America and Europe.
Required satellite spacing creates a limited number of geostationary orbital locations. Satellites using common portions of the frequency spectrum must be spaced far enough apart to prevent interference with adjacent satellites. This spacing is commonly quantified in degrees of angular spacing as measured from the center of the Earth. For example, direct broadcast satellites (DBS) typically require at least 9 degrees of angular spacing, while fixed satellite service (FSS) typically requires at least 2 degrees of angular spacing between adjacent satellites. As the required spacing increases, the number of available orbital locations decreases. High-demand areas, such as North America and Europe, have an insufficient number of available geostationary orbital locations to meet future communications needs.
As available orbital locations are filled with satellites, the amount of frequency spectrum allocated for use by the satellites becomes a second factor limiting the expansion of satellite communications. The International Telecommunication Union (ITU) has allocated portions of the frequency spectrum for use in satellite communications. Satellite communications systems currently use the C-band, the Ku-band, and/or the Ka-band of the frequency spectrum. The amount of data transmitted and/or received by a satellite is limited to the bandwidth provided by these frequency bands. Once the available bandwidth has been used, other solutions must be devised to provide additional communications capacity.
Another set of difficulties arises when an operator wishes to replace an existing communications system with a new one. Typically, it is not feasible for the operator to shut down operation completely and replace or modify all existing equipment for the new communications system. For example, a change in a DBS system would require all current customers to update their reception equipment to be compatible with the new system. Customers may not be willing or able to update their equipment within a timeframe desired by the operator. Therefore, any new communications system must be able to provide a smooth transition path for operators.
Accordingly, a need exists for a satellite communications system that can provide sufficient capacity to meet future communications needs. Such a system must provide the additional communications capacity while taking into account the limitations imposed by available orbital locations and allocated frequency spectrum. The system must also take into consideration the possible difficulties involved when transitioning to a new communications system.